Intervalence transverse-electric mode terahertz lasing without population inversion

This paper applies the Keldysh nonequilibrium Green's-function formalism to introduce the concept of k-space filtering due to the strong localization of the intervalence transverse-electric (TE) dipole moments in III-V quantum wells. The effect enhances the gain without inversion for holes under nonequilibrium conditions that results from the strong valence-band nonparabolicity and can potentially lead to terahertz lasing at high temperatures. Numerical solutions of the integrodifferential susceptibility equation derived from the microscopic carrier Green's functions are discussed. The approach consistently takes into account the interplay of nonequilibrium nonparabolicity many-body, and dephasing effects as well as the detrimental influence of cross absorption due to the multiple subband transitions.